package main

import (
	"fmt"
	"runtime"
	"time"
)

type buffer struct {
	a int
	b []byte
	c int
}

func main() {
	c := make(chan bool)
	const n = 500
	for i := 0; i < n; i++ {
		go func() {
			myc := c
			for {
				var b buffer
				<-myc     // pass by here once, then block forever.
				myc = nil

				// This buffer should only survive for the next 2 lines
				// and the call to foo. Once the for loop returns to
				// the "var b buffer" line, b.b should be zero, and the
				// GC should have collected it.
				b.b = make([]byte, 2 << 20)
				foo(b)

				// This doesn't even help:
				// b.b = nil
			}
		}()
	}
	for i := 0; i < n; i ++ {
		select {
		case c <- true:
		default:
		}
		runtime.GC()
		var s runtime.MemStats
		runtime.ReadMemStats(&s)
		fmt.Printf("alloc (still in use): %d\n", s.Alloc)
		fmt.Printf("                 sys: %d\n", s.Sys)
		fmt.Printf("              num gc: %d\n", s.NumGC)
		fmt.Println()
		time.Sleep(1 * time.Second)
	}
}

func foo(b buffer) {
	// nothing
}